Security Best Practices

OpenShell enforces sandbox security across four layers: network, filesystem, process, and inference. This page documents every configurable control, its default, what it protects, and the risk of relaxing it.

For the full policy YAML schema, refer to the Policy Schema Reference. For the architecture of each enforcement layer, refer to How OpenShell Works.

See also

If you use NemoClaw to run OpenClaw assistants, its Security Best Practices guide covers additional entrypoint-level controls, policy presets, provider trust tiers, and posture profiles specific to the NemoClaw blueprint.

Enforcement Layers

OpenShell applies security controls at two enforcement points. OpenShell locks static controls at sandbox creation and requires destroying and recreating the sandbox to change them. You can update dynamic controls on a running sandbox with openshell policy set.

Layer	What it protects	Enforcement point	Changeable at runtime
Network	Unauthorized outbound connections and data exfiltration.	CONNECT proxy + OPA policy engine	Yes. Use openshell policy set or operator approval in the TUI.
Filesystem	System binary tampering, credential theft, config manipulation.	Landlock LSM (kernel level)	No. Requires sandbox re-creation.
Process	Privilege escalation, fork bombs, dangerous syscalls.	Seccomp BPF + privilege drop (setuid/setgid)	No. Requires sandbox re-creation.
Inference	Credential exposure, unauthorized model access.	Proxy intercept of inference.local	Yes. Use openshell inference set.

Network Controls

The CONNECT proxy and OPA policy engine enforce all network controls at the gateway level.

Deny-by-Default Egress

Every outbound connection from the sandbox goes through the CONNECT proxy. The proxy evaluates each connection against the OPA policy engine. If no network_policies entry matches the destination host, port, and calling binary, the proxy denies the connection.

Aspect	Detail
Default	All egress denied. Only endpoints listed in network_policies can receive traffic.
What you can change	Add entries to network_policies in the policy YAML. Apply statically at creation (--policy) or dynamically (openshell policy set).
Risk if relaxed	Each allowed endpoint is a potential data exfiltration path. The agent can send workspace content, credentials, or conversation history to any reachable host.
Recommendation	Add only endpoints the agent needs for its task. Start with a minimal policy and use denied-request logs (openshell logs <name> --source sandbox) to identify missing endpoints.

Network Namespace Isolation

The sandbox runs in a dedicated Linux network namespace with a veth pair. All traffic routes through the host-side veth IP (10.200.0.1) where the proxy listens. Even if a process ignores proxy environment variables, it can only reach the proxy.

Aspect	Detail
Default	Always active. The sandbox cannot bypass the proxy at the network level.
What you can change	This is not a user-facing knob. OpenShell always enforces it in proxy mode.
Risk if bypassed	Without network namespace isolation, a process could connect directly to the internet, bypassing all policy enforcement.
Recommendation	No action needed. OpenShell enforces this automatically.

Binary Identity Binding

The proxy identifies which binary initiated each connection by reading /proc/<pid>/exe (the kernel-trusted executable path). It walks the process tree for ancestor binaries and parses /proc/<pid>/cmdline for script interpreters. The proxy SHA256-hashes each binary on first use (trust-on-first-use). If someone replaces a binary mid-session, the hash mismatch triggers an immediate deny.

Aspect	Detail
Default	Every network_policies entry requires a binaries list. Only listed binaries can reach the associated endpoints. Binary paths support glob patterns (* for one path component, ** for recursive).
What you can change	Add binaries to an endpoint entry. Use glob patterns for directory-scoped access (for example, /sandbox/.vscode-server/**).
Risk if relaxed	Broad glob patterns (like /**) allow any binary to reach the endpoint, defeating the purpose of binary-scoped enforcement.
Recommendation	Scope binaries to the specific executables that need each endpoint. Use narrow globs when the exact path varies (for example, across Python virtual environments).

L4-Only vs L7 Inspection

The protocol field on an endpoint controls whether the proxy inspects individual HTTP requests inside the tunnel.

Aspect	Detail
Default	Endpoints without a protocol field use L4-only enforcement: the proxy checks host, port, and binary, then relays the TCP stream without inspecting payloads.
What you can change	Add protocol: rest to enable per-request HTTP inspection. Pair it with rules (fine-grained method and path control) or access presets (full, read-only, read-write).
Risk if relaxed	L4-only endpoints allow the agent to send any data through the tunnel after the initial connection is permitted. The proxy cannot see HTTP methods, paths, or bodies. Adding access: full with protocol: rest enables inspection but permits all methods and paths, providing observability without restriction.
Recommendation	Use protocol: rest with specific rules for APIs where you want method and path control. Use access: read-only for read-only endpoints. Omit protocol for non-HTTP protocols (WebSocket, gRPC streaming).

Enforcement Mode (audit vs enforce)

When protocol: rest is active, the enforcement field controls whether the proxy blocks or logs rule violations.

Aspect	Detail
Default	audit. The proxy logs violations but forwards traffic.
What you can change	Set enforcement: enforce to block requests that do not match any rules entry. Denied requests receive a 403 Forbidden response with a JSON body describing the violation.
Risk if relaxed	audit mode provides visibility but does not prevent unauthorized actions. An agent can still perform write or delete operations on an API even if the rules would deny them.
Recommendation	Start with audit to understand traffic patterns and verify that rules are correct. Switch to enforce once you have validated that the rules match the intended access pattern.

TLS Handling

The proxy auto-detects TLS on every tunnel by peeking the first bytes. When a TLS ClientHello is detected, the proxy terminates TLS transparently using a per-sandbox ephemeral CA. This enables credential injection and L7 inspection without explicit configuration.

Aspect	Detail
Default	Auto-detect and terminate. OpenShell generates the sandbox CA at startup and injects it into the process trust stores (NODE_EXTRA_CA_CERTS, SSL_CERT_FILE, REQUESTS_CA_BUNDLE, CURL_CA_BUNDLE).
What you can change	Set tls: skip on an endpoint to disable TLS detection and termination for that endpoint. Use this for client-certificate mTLS to upstream or non-standard binary protocols.
Risk if relaxed	tls: skip disables credential injection and L7 inspection for that endpoint. The proxy relays encrypted traffic without seeing the contents.
Recommendation	Use auto-detect (the default) for most endpoints. Use tls: skip only when the upstream requires the client’s own TLS certificate (mTLS) or uses a non-HTTP protocol.

SSRF Protection

After OPA policy allows a connection, the proxy resolves DNS and rejects connections where the resolved IP is internal (loopback, link-local, or RFC 1918 private).

Aspect	Detail
Default	The proxy blocks all private IPs. Loopback (127.0.0.0/8) and link-local (169.254.0.0/16) remain blocked even with allowed_ips.
What you can change	Add allowed_ips (CIDR notation) to an endpoint to permit connections to specific private IP ranges.
Risk if relaxed	Without SSRF protection, a misconfigured policy could allow the agent to reach cloud metadata services (169.254.169.254), internal databases, or other infrastructure endpoints through DNS rebinding.
Recommendation	Use allowed_ips only for known internal services. Scope the CIDR as narrowly as possible (for example, 10.0.5.20/32 for a single host). Loopback and link-local are always blocked regardless of allowed_ips.

Operator Approval

When the agent requests an endpoint not in the policy, OpenShell blocks it and surfaces the request in the TUI for operator review. The system merges approved endpoints into the sandbox’s policy as a new durable revision.

Aspect	Detail
Default	Enabled. The proxy blocks unlisted endpoints and requires approval.
What you can change	Approved endpoints persist across sandbox restarts within the same sandbox instance. They reset when the sandbox is destroyed and recreated.
Risk if relaxed	Approving an endpoint permanently widens the running sandbox’s policy. Review each request before approving.
Recommendation	Use operator approval for exploratory work. For recurring endpoints, add them to the policy YAML with appropriate binary and path restrictions. To reset all approved endpoints, destroy and recreate the sandbox.

Filesystem Controls

Landlock LSM restricts which paths the sandbox process can read or write at the kernel level.

Landlock LSM

Landlock enforces filesystem access at the kernel level. Paths listed in read_only receive read-only access. Paths listed in read_write receive full access. All other paths are inaccessible.

Aspect	Detail
Default	compatibility: best_effort. Uses the highest kernel ABI available. The system skips missing paths with a warning. If the kernel does not support Landlock, the sandbox continues without filesystem restrictions.
What you can change	Set compatibility: hard_requirement to abort sandbox startup if Landlock is unavailable or any configured path cannot be opened.
Risk if relaxed	On kernels without Landlock (pre-5.13), or when all paths fail to open, the sandbox runs without kernel-level filesystem restrictions. The agent can access any file the process user can access.
Recommendation	Use best_effort for development. Use hard_requirement in environments where any gap in filesystem isolation is unacceptable. Run on Ubuntu 22.04+ or any kernel 5.13+ for Landlock support.

Read-Only vs Read-Write Paths

The policy separates filesystem paths into read-only and read-write groups.

Aspect	Detail
Default	System paths (/usr, /lib, /etc, /var/log) are read-only. Working paths (/sandbox, /tmp) are read-write. /app is conditionally included if it exists.
What you can change	Add or remove paths in filesystem_policy.read_only and filesystem_policy.read_write.
Risk if relaxed	Making system paths writable lets the agent replace binaries, modify TLS trust stores, or change DNS resolution. Validation rejects broad read-write paths (like /).
Recommendation	Keep system paths read-only. If the agent needs additional writable space, add a specific subdirectory.

Path Validation

OpenShell validates policies before they take effect.

Constraint	Behavior
Paths must be absolute (start with /).	Rejected with INVALID_ARGUMENT.
Paths must not contain .. traversal.	Rejected with INVALID_ARGUMENT.
Read-write paths must not be overly broad (for example, / alone).	Rejected with INVALID_ARGUMENT.
Each path must not exceed 4096 characters.	Rejected with INVALID_ARGUMENT.
Combined read_only + read_write paths must not exceed 256.	Rejected with INVALID_ARGUMENT.

Process Controls

The sandbox supervisor drops privileges, applies seccomp filters, and enforces process-level restrictions during startup.

Privilege Drop

The sandbox process runs as a non-root user after explicit privilege dropping.

Aspect	Detail
Default	run_as_user: sandbox, run_as_group: sandbox. The supervisor calls setuid()/setgid() with post-condition verification: confirms the effective UID/GID match the target and that setuid(0) fails (root cannot be re-acquired).
What you can change	Set run_as_user and run_as_group in the process section. Validation rejects root (root or 0).
Risk if relaxed	Running as a higher-privilege user increases the impact of container escape vulnerabilities.
Recommendation	Keep the sandbox user. Do not attempt to set root.

Seccomp Filters

A BPF seccomp filter restricts which socket domains the sandbox process can use.

Aspect	Detail
Default	The filter allows AF_INET and AF_INET6 (for proxy communication) and blocks AF_NETLINK, AF_PACKET, AF_BLUETOOTH, and AF_VSOCK with EPERM. The sandbox sets PR_SET_NO_NEW_PRIVS before applying the filter.
What you can change	This is not a user-facing knob. OpenShell enforces it automatically.
Risk if relaxed	AF_NETLINK allows manipulation of routing tables and firewall rules. AF_PACKET enables raw packet capture. AF_VSOCK enables VM socket communication.
Recommendation	No action needed. OpenShell enforces this automatically.

Enforcement Application Order

The sandbox supervisor applies enforcement in a specific order during process startup. This ordering is intentional: privilege dropping needs /etc/group and /etc/passwd, which Landlock subsequently restricts.

1. Network namespace entry (setns).

2. Privilege drop (initgroups + setgid + setuid).

3. Landlock filesystem restrictions.

4. Seccomp socket domain filters.

Inference Controls

OpenShell routes all inference traffic through the gateway to isolate provider credentials from the sandbox.

Routed Inference through inference.local

The proxy intercepts HTTPS CONNECT requests to inference.local and routes matching inference API requests through the sandbox-local router. The agent never receives the provider API key.

Aspect	Detail
Default	Always active. The proxy handles inference.local before OPA policy evaluation. The gateway injects credentials on the host side.
What you can change	Configure inference routes with openshell inference set.
Risk if bypassed	If an inference provider’s host is added directly to network_policies, the agent could reach it with a stolen or hardcoded key, bypassing credential isolation.
Recommendation	Do not add inference provider hosts to network_policies. Use OpenShell inference routing instead.

Gateway Security

The gateway secures communication between the CLI, sandbox pods, and external clients with mutual TLS and token-based authentication.

mTLS

Communication between the CLI, sandbox pods, and the gateway is secured by mutual TLS. OpenShell generates a cluster CA at bootstrap and distributes it through Kubernetes secrets.

Aspect	Detail
Default	mTLS required. Both client and server present certificates that the cluster CA signed.
What you can change	Enable dual-auth mode (allow_unauthenticated=true) for Cloudflare Tunnel deployments, or disable TLS entirely for trusted reverse-proxy setups.
Risk if relaxed	Dual-auth mode accepts clients without certificates and defers authentication to the HTTP layer (Cloudflare JWT). Disabling TLS removes transport-level authentication entirely.
Recommendation	Use mTLS (the default) unless deploying behind Cloudflare or a trusted reverse proxy.

SSH Tunnel Authentication

SSH connections to sandboxes pass through the gateway’s HTTP CONNECT tunnel with token-based authentication and HMAC-SHA256 handshake verification (NSSH1 protocol).

Aspect	Detail
Default	Session tokens expire after 24 hours. Concurrent connections are limited to 10 per token and 20 per sandbox.
What you can change	Configure ssh_session_ttl_secs. Set to 0 for no expiry.
Risk if relaxed	Longer TTLs or no expiry increase the window for stolen token reuse. Higher connection limits increase the blast radius of a compromised token.
Recommendation	Keep the 24-hour default. Monitor connection counts through the TUI.

Common Mistakes

The following patterns weaken security without providing meaningful benefit.

Mistake	Why it matters	What to do instead
Omitting protocol: rest on REST API endpoints	Without protocol: rest, the proxy uses L4-only enforcement. It allows the TCP stream through after checking host, port, and binary, but cannot inspect individual HTTP requests.	Add protocol: rest with specific rules to enable per-request method and path control.
Using access: full when finer rules would suffice	access: full with protocol: rest enables inspection but allows all HTTP methods and paths.	Use access: read-only or explicit rules to restrict what the agent can do at the HTTP level.
Adding endpoints permanently when operator approval would suffice	Adding endpoints to the policy YAML makes them permanently reachable across all instances.	Use operator approval. Approved endpoints persist within the sandbox instance but reset on re-creation.
Using broad binary globs	A glob like /** allows any binary to reach the endpoint, defeating binary-scoped enforcement.	Scope globs to specific directories (for example, /sandbox/.vscode-server/**).
Skipping TLS termination on HTTPS APIs	Setting tls: skip disables credential injection and L7 inspection.	Use the default auto-detect behavior unless the upstream requires client-certificate mTLS.
Setting enforcement: enforce before auditing	Jumping to enforce without first running in audit mode risks breaking the agent’s workflow.	Start with audit, review the logs, and switch to enforce once you have validated the rules.

Related Topics

• Customize Sandbox Policies for applying and iterating on sandbox policies.

• Policy Schema Reference for the full field-by-field YAML reference.

• Default Policy Reference for the built-in default policy breakdown.

• Gateway Authentication for gateway authentication details.

• How OpenShell Works for the system architecture.

• NemoClaw Security Best Practices for entrypoint-level controls (capability drops, PATH hardening, build toolchain removal), policy presets, provider trust tiers, and posture profiles.